1. Field of the Invention
The present invention relates generally to a novel type of information carrier, on which information can be stored in the form of diffraction structures. The information carrier according to the present invention can be read, for example, by being drawn manually through a reading device.
2. Description of Related Art
Plastic cards as information carriers are ubiquitous nowadays. As a consequence of increasing data processing by machine, a person typically has a series of plastic cards with which he can authenticate himself. Examples which may be mentioned include company identity cards, medical insurance cards, credit, Eurocheque and debit cards.
Particularly widespread is the ID-1 format, which is characterized in the ISO/IEC 7810 Standard (“credit card format”). It has a convenient size and can be accommodated in purses. There are many card readers which are based on this format.
Machine-readable information can be stored on plastic cards in various ways. For instance, optically in the form of optically readable letters (OCR=Optical Character Recognition), bar or matrix codes, magnetically in a magnetic strip or electronically in a chip. However, the aforementioned storage methods only permit the storage of a few bytes (OCR) to kilobytes (chip). The greatest storage capacity in plastic cards is achieved nowadays by optical memory cards.
In WO8808120 (A1) and EP0231351 (A1), optical memory cards are described in which data is exposed photographically into a silver halide film which is applied to the plastic cards. The data can be written and read with a laser. In WO 8808120 (A1), a device is described with which the film can be written and read. The data is present digitally in the form of data points. The data points exhibit a different reflectance as compared with the surroundings and in this way can be read with the aid of a laser beam and a photodetector.
A disadvantage with this type of card and card reader is that the card must be positioned exactly with respect to read beam and detector in order to read the data. In order to read out the individual data points one after another, the card must also be moved relative to a read beam and a detector in such a way that the read beam strikes the data points accurately. This requires a complex card reader having a high positioning accuracy. Moreover, the data density on the card is restricted to the dimension of the positioning accuracy during reading. If the data points are present more densely than the positioning accuracy of the read beam, the individual data points are difficult or even impossible to detect.
When bar code or magnetic strip cards are used, it is possible to draw the card through a card guide in order to read it. Data is read as the card is drawn through manually. In such cards, mechanical positioning of the read head relative to the card is not necessary.
Such a draw-through system for magnetic strip cards is described, for example, in U.S. Pat. No. 5,128,524 (A1).
The implementation of a manual card draw-through system for reading data which is stored on a plastic card is possible in the case of magnetic strips and bar codes, since the data density (quantity of bytes per unit area) is so low that the positioning of the storage medium in relation to the read head is tolerant with respect to the changes which occur during the manual card guidance.
In the optical memory cards described above, the data structures are smaller. Manual positioning of the card in relation to the read head is therefore generally no longer possible.
However, it would be desirable to be able to read optical memory cards having a higher storage capacity than is usual in the case of magnetic strip or bar code cards with the aid of a card draw-through system that can be operated manually.
Advantages of manual card guidance include: 1) greater convenience for the user, since the user does not have to let go of the card, and increased speed of the entire reading process and, 2) reduced production costs of the device, since it is possible to eliminate expensive mechanical positioning, and 3) greater ruggedness of the device.